An existing evolved packet system (EPS) includes user equipment (UE), an evolved universal terrestrial radio access network (EUTRAN), and a core network (CN). Refer to a schematic architectural diagram of an EPS shown in FIG. 1. The EUTRAN may be specifically implemented by evolved node B (eNB); the CN mainly includes an mobility management entity (MME), an serving general packet radio service supporting node (SGSN), an home subscriber server (HSS), an serving gateway (S-GW), a packet data network gateway (P-GW), and a policy and charging rules function (PCRF).
When the user equipment attaches to the network, a bearer is established by using signaling exchange between a radio access network element, a mobility management network element, the serving gateway, and the packet data gateway, so as to transmit data by using the bearer. Because the existing EPS system is based on an IP mechanism, when the EPS system is used to send data, the radio access network element encapsulates an IP data packet into a general packet radio service tunnelling protocol for the user plane (GTP-U) data packet and then sends the GTP-U data packet to the serving gateway; the serving gateway sends the GTP-U data packet to the packet data gateway; and the packet data gateway decapsulates the GTP-U data packet into an IP data packet and then performs forwarding processing. Correspondingly, when the EPS system is used to receive data, after receiving an IP data packet, the packet data gateway encapsulates the IP data packet into a GTP-U data packet and then sends the GTP-U data packet to the serving gateway; the serving gateway forwards the GTP-U data packet to the radio access network element; and the radio access network element decapsulates the GTP-U data packet into an IP data packet and then sends the IP data packet to the user equipment.
An IP header needs to be added when data is encapsulated into an IP data packet. If UE only needs to transmit small data of an extremely small data volume, where, for example, the small data is a message generated by an application program, including a status message, a location message, a heartbeat message, a real-time message, and the like, or the small data is SIP (Session Initiation Protocol, Session Initiation Protocol) signaling, a Push (push) message, a control message, and the like, adding an IP header in front of the small data will decrease a data payload of an IP data packet, which decreases data transmission efficiency. For example, if the small data is 10 bytes, while a fixed size of the IP header is 20 bytes, the percentage of the small data is low in the IP packet, which decreases the data transmission efficiency.